Process for obtaining low free monomer levels in a block copolymer emulsion prepared with (reverse) iodine transfer polymerisation

ABSTRACT

A process for obtaining an aqueous emulsion comprising a block copolymer by the solution polymerisation of vinyl monomers to obtain block [B] in the presence of a) a radical precursor; and b) an iodine atom containing block [A]; where block [A] and [B] together comprise 0 to 2 wt % of methacrylic acid; where block [A] and block [B] together comprise ≧2.5 wt % of vinyl monomers bearing ionic or potentially ionic water-dispersing groups not including methacrylic acid; and performing a post polymerisation reaction on the block copolymer emulsion obtained in step II; and wherein said aqueous emulsion has a free vinyl monomer level &lt;1000 ppm when having a solids content of ≧20 wt %.

The present invention concerns a process for obtaining low free monomerlevels in an aqueous emulsion comprising a block copolymer where theblock copolymer is prepared with (reverse) iodine transferpolymerisation, the aqueous emulsion comprising a block copolymerobtained by the process and the use of the aqueous emulsion for coating,adhesive and printing ink compositions.

Control over polymer chain architecture, resulting in for instance blockcopolymers, may be very beneficial in achieving improved properties whenthe polymer is used for instance in coating, adhesive and printing inkcompositions. Several polymerisation techniques, also known as “livingpolymerisation techniques” have been found to be able to deliver suchkind of control, such as for example Reversible Addition FragmentationChain Transfer (RAFT), Atom Transfer Radical Polymerisation (ATRP) andNitroxide Mediated Controlled Radical Polymerisations (NRP). Howevereach of these techniques have their disadvantages. With ATRP it iscurrently not possible to incorporate acid functional monomers; NRP canonly be done effectively at temperatures above 110° C., and RAFT yieldsproblems with the ultimate RAFT unit that should be removed because ofthe toxicity and odour of these units.

It has been found that (reverse) Iodine Transfer Polymerisation (RITP)can circumvent all of these problems. RITP may be done at practicaltemperatures of below 100° C., allowing polymerisations in water and orsolution. There are no restrictions of the type of monomer used (forexample (meth)acrylic esters, styrene), nor any restriction on thefunctionality of the monomer (for example ionic functional groups and orcrosslinking functional groups). Finally, as the active ingredient is aniodine atom group used at low concentrations, the toxicity profileappears to be more favourable.

RITP is described in for example U.S. Pat. No. 7,078,473 which disclosesa radical polymerisation process for the preparation of halogenatedpolymers and block copolymers using molecular iodine and aradical-generating agent.

US 2007/0066781 discloses a process for preparing iodinated substanceshaving a molecular mass of less than 2000 using molecular iodine and aradical-generating agent.

WO 2004/009648 and US 2004/0054108 disclose a method for making a blockor gradient copolymer comprising a step of radically polymerising amixture of monomers to a iodine atom-containing polymeric compound,wherein the iodine atom-containing polymeric compound comprises at least50 mol % of methacrylate monomers.

WO 2004/009644 discloses a method for making a methacrylateunit-containing polymer with a polydispersity of less than 1.7 in thepresence of a radical precursor and iodine or sulphonyl iodide.

EP 0947527 discloses a controlled free-radical polymerisation processfor forming waterborne block copolymers by an emulsion polymerisationprocess using for example degenerative iodine transfer polymerisationprocesses.

WO 03/097704 discloses radical polymerisation methods, including the useof molecular iodine, for making halogenated polymers, including blockcopolymers where at least one block is halogenated.

In RITP molecular iodine is added to a radical polymerisation causingthe radicals to be trapped with iodine groups.

R•+I₂→R—I

These iodine functional polymer chains will then act as chain transferagents for growing radical chains. The former iodine functional chainbecomes an active radical, while the former active radical becomesiodine end capped.

R—O+R′•→R•+R′—I

Hence, a growing radical chain has two options, it can propagate byadding monomer units or it can undergo chain transfer by reacting with aiodine functional compound. In this way the radical polymerisationbecomes a controlled polymerisation.

However a disadvantage with RITP is that it yields a very high freemonomer level, i.e. the rate of monomer conversion is less than 99.5%.The lowest reported free vinyl monomer level, within a practical timeframe, is 4,000 ppm (or a vinyl monomer conversion of 99% at 40%solids). Most of the reports on free vinyl monomer levels are, however,significantly higher at around 25,000 ppm (or a conversion of only 97%).

We have now surprisingly found that we can make aqueous emulsionscomprising polymer structures obtained through controlledpolymerisations using RITP, having a low free monomer content.

According to the invention the provided a process for obtaining an anaqueous emulsion comprising a block copolymer, which process comprisesthe following steps:

-   -   I) solution polymerisation of vinyl monomers to obtain block [B]        in the presence of        -   a) a radical precursor; and        -   b) an iodine atom containing block [A]; to obtain a block            copolymer comprising at least block [A] and a different            block [B];    -   where block [A] and [B] together comprise 0 to 2 wt % of        methacrylic acid;    -   where block [A] comprises 0 to 25 wt % of vinyl monomers bearing        ionic or potentially ionic water-dispersing groups not including        methacrylic acid;    -   where block [B] comprises 0 to 25 wt % of vinyl monomers bearing        ionic or potentially ionic water-dispersing groups not including        methacrylic acid;    -   where block [A] and block [B] together comprise ≧2.5 wt % of        vinyl monomers bearing ionic or potentially ionic        water-dispersing groups not including methacrylic acid;    -   II) emulsification of the block copolymer obtained in step I);    -   III) performing a post polymerisation reaction on the block        copolymer emulsion obtained in step II; and    -   wherein said aqueous emulsion has a free vinyl monomer level        <1000 ppm when having a solids content of ≧20 wt %.

The free monomer level may be measured by gas chromatography (GC). Afree monomer level of 1000 ppm at 40% solids is equivalent to a monomerconversion of 99.75%. This is considered as an acceptable level of freemonomers in a general emulsion. A free monomer level of 500 ppm at 40%solids is equivalent to a monomer conversion of 99.87%. This isconsidered as a good level of free monomers in a general emulsion. Afree monomer level of ≦100 ppm at 40% solids is equivalent to a monomerconversion of ≧99.98%. This is considered as an excellent level of freemonomers in a general emulsion.

Preferably the aqueous emulsion has a free vinyl monomer level <1000 ppmwhen having a solids content of 35 +/−15 wt %, more preferably 35+/−10wt % and most preferably 35+/−5 wt %.

Preferably the aqueous emulsion has a free vinyl monomer level ≦800 ppm,more preferably ≦500 ppm, most preferably ≦400 ppm and especially ≦300ppm when having a solids content of ≧20 wt %.

Preferably the iodine atom containing block [A] is selected from thegroup consisting of vinyl polymers, polyurethanes, polyesters,polyethers, polyolefins, alkyds, and or mixtures thereof.

More preferably the iodine atom containing block [A] is obtained by thepolymerisation of vinyl monomers in the presence of

a) a radical precursor and

b) iodine or an iodine transfer agent.

By iodine is meant molecular iodine and compounds that can form iodinesuch as I₃ ⁻, N-iodosuccinimide etc. The preparation of an iodine atomcontaining intermediate vinyl polymer is described in WO 04/009648.

The polymerisation of vinyl monomers in step I in the presence of theiodine atom containing block [A] is carried out by solutionpolymerisation. Preferably the polymerisation of vinyl monomers in stepI is carried out by solution polymerisation in an organic solvent.

The resultant copolymer is a block copolymer with block [A] and thevinyl monomers polymerised in step I become block [B] and any optionalfurther blocks [C] depending on the type of polymerisation carried out,such as multi-stage polymerisations. The block copolymer contains afirst block [A], a second block [B] and optionally one or more blocks[C].

Preferably the number average molecular weight of block [A] is in therange of from 200 to 60,000 g/mol, more preferably from 500 to 30,000g/mol and most preferably from 700 to 15,000 g/mol.

Preferably the number average molecular weight of block [B] is in rangeof from 200 to 60,000 g/mol, more preferably from 500 to 30,000 g/moland most preferably from 700 to 15,000 g/mol.

Preferably the block copolymer has a PDi (PDi=Mw/Mn) in the range offrom 0.1 to 4, more preferably 1 to 3 and especially 1 to 2.

Preferably the block copolymer has an average particle size of ≦600 nm,as determined by light scattering, more preferably ≦300 nm and mostpreferably ≦250 nm.

Preferably the post-polymerisation reaction to reduce the free monomerlevel is done with a redox couple comprising an organic or inorganicperoxide or hydroperoxide and a reducing agent. The use of intermediatereactants such as iron ions is optional. Preferred hydroperoxides aret-butyl hydroperoxide, cumyl hydroperoxide, 1,1,3,3-tetramethylbutylhydroperoxide, isopropylcumyl hydroperoxide, and hydrogenperoxide.Preferred inorganic peroxides are sodium, potassium or ammonium peroxidesalts. Preferred organic peroxides are dilauryl peroxide, dibenzoylperoxide, t-butyl-per-2-ethyl hexanoate, t-butyl perbenzoate, dicumylperoxide, di-t-butyl peroxide. Preferred reducing agents are ascorbicacid, iso-ascorbic acid, sodium metabisulphite, sodium dithionite andsodium formaldehyde sulfoxylate.

The post-polymerisation reaction to reduce the free monomer level mayalso be carried out by the reaction of an initiator selected from thegroup consisting of azo functional initiators, organic peroxides,inorganic peroxides or mixtures thereof.

Preferred azo functional initiators are 2,2′-azodi isobutyronitrile,2,2′-azodi(2-methylbutyronitrile), VAZO® 68 WSP, VAZO® 56, VAZO® 52 (ex.DuPont) or VA-086 (ex. WAKO Chemicals).

More than one post-polymerisation reaction may be carried out.

Blocks [A] and [B] should be different. The difference can be in the Tgof the blocks, the hydrophilic or hydrophobic nature of the monomers orthe concentration of functional monomers within the blocks orcombinations thereof.

Where the difference between blocks [A] and [B] is Tg, preferably one ofthe blocks has a Tg≦20° C., more preferably ≦0° C. and most preferably−15° C., while the other block preferably has a Tg of ≧10° C., morepreferably ≧25° C., most preferably ≧30° C., and especially ≧50° C. Mostpreferably the difference in Tg between blocks [A] and [B] is ≧40° C.

Where the difference between blocks [A] and [B] is the hydrophilic orhydrophobic nature of the blocks, then one of the blocks preferablycontains ≧5 wt % of hydrophilic groups (for example acidic or hydroxylfunctional groups), more preferably ≧10 wt % and especially ≧20 wt %,while the other block would contain ≦2 wt %, more preferably ≦1 wt % andmost preferably no hydrophilic groups. It is also possible to induce adifference in hydrophilic or hydrophobic nature between the blocks byincorporating very hydrophobic monomers in the hydrophobic segment. Suchmonomers can be for instance 2-ethyl hexyl(meth)acrylate, lauryl(meth)acrylate, stearyl (meth)acrylate, styrene or modified styrenemonomers, or a-methyl styrene. When such very hydrophobic monomers areused in the hydrophobic block, this block may still contain lowconcentrations of hydrophilic monomers.

Blocks [A] and [B] may contain functional monomers. These can be 1) acidmonomers for enhanced stability and/or adhesion, 2) monomers that maytypically yield improved adhesion, 3) crosslinking monomers that alsomay improve adhesion properties, 4) quaternary ammonium groups forantimicrobial activity, anti static properties or reduced grain raising,or 5) monomers that may induce semi-crystalline behaviour. If any ofthese monomers are used it is preferred that blocks [A] and [B] comprisedifferent functionalities or if similar functionalities then indifferent concentrations. When the emulsion is stabilised with anionicgroups from the block copolymer the acid value of the block copolymer ispreferably ≦120 mg KOH/g of solid polymer, more preferably ≦80 mg KOH/g,even more preferably ≦60 mg KOH/g, most preferably ≦50 mg KOH/g andespecially in the range of from 2 to 50 mg KOH/g of solid polymer.

Block [B] and block [A] (if block [A] is a vinyl polymer), are derivedfrom free-radically polymerisable olefinically unsaturated monomers,which are also usually referred to as vinyl monomers, and can containpolymerised units of a wide range of such vinyl monomers, especiallythose commonly used to make binders for the coatings industry.

Examples of vinyl monomers which may be used to form the blocks includebut are not limited to olefinically unsaturated monomers such as1,3-butadiene, isoprene, divinyl benzene, aromatic vinyl monomers suchas styrene, α-methyl styrene; vinyl monomers such as acrylonitrile,methacrylonitrile; vinyl halides such as vinyl chloride; vinylidenehalides such as vinylidene chloride; vinyl esters such as vinyl acetate,vinyl propionate, vinyl laurate; vinyl esters of versatic acid such asVeoVa 9 and VeoVa 10 (VeoVa is a trademark of Resolution); heterocyclicvinyl compounds; alkyl esters of mono-olefinically unsaturateddicarboxylic acids such as di-n-butyl maleate and di-n-butyl fumarateand, in particular, esters of acrylic acid and methacrylic acid offormula CH₂═CR⁵—COOR⁴ wherein R⁵ is H or methyl and R⁴ is optionallysubstituted C₁ to C₂₀, more preferably C₁ to C₈, alkyl, cycloalkyl, arylor (alkyl)aryl which are also known as acrylic monomers, examples ofwhich are methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, propyl(meth)acrylate (all isomers), and hydroxyalkyl (meth)acrylates such ashydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,4-hydroxybutyl (meth)acrylate and their modified analogues like ToneM-100 (Tone is a trademark of Union Carbide Corporation).

The vinyl monomers may also include vinyl monomers carrying functionalgroups as exemplified below. These may be in-chain, pendant or terminalgroups.

Water-dispersing functional groups provide the facility ofself-dispersibility, stability, solubility in water and/or a substrate.The water dispersing groups may be ionic, potentially ionic, nonionic ora mixture of such water-dispersing groups.

Preferred vinyl monomers providing nonionic water-dispersing groupsinclude alkoxy polyethylene glycol (meth)acrylates, hydroxy polyethyleneglycol (meth)acrylates, alkoxy prolyproplene glycol (meth)acrylates andhydroxy polypropylene glycol (meth)acrylates, preferably having a numberaverage molecular weight of from 350 to 3,000.

Vinyl monomers providing ionic or potentially ionic water-dispersinggroups include vinyl monomers providing anionic or potentially anionic,cationic or potentially cationic water-dispersing groups.

Preferred vinyl monomers providing anionic or potentially anionicwater-dispersing groups include acrylic acid, itaconic acid, maleicacid, β-carboxyethyl acrylate, monoalkyl maleates (for examplemonomethyl maleate and monoethyl maleate), citraconic acid,styrenesulphonic acid, vinylbenzylsulphonic acid, vinylsulphonic acid,acryloyloxyalkyl sulphonic acids (for example acryloyloxymethylsulphonic acid), 2-acrylamido-2-alkylalkane sulphonic acids (for example2-acrylamido-2-methylethanesulphonic acid),2-methacrylamido-2-alkylalkane sulphonic acids (for example2-methacrylamido-2-methylethanesulphonic acid),mono(acryloyloxyalkyl)phosphates (for example,mono(acryloyloxyethyl)phosphate and mono(3-acryloyloxypropyl)phosphates)and mono(methacryloyloxyalkyl)phosphates.

The anionic or potentially anionic water-dispersing groups of the blockcopolymer may be neutralised before during or after the emulsificationstep II. Preferred neutralising agents include ammonia, trimethylamine,dimethyl ethanol amine, dimethyl butyl amine, sodium hydroxide,potassium hydroxide and or lithium hydroxide.

Preferred vinyl monomers providing quaternary ammonium and/orquaternisable amine functional group include but are not limited to2-trimethylammoniumethyl (meth)acrylate chloride, 2-dimethylaminoethyl(meth)acrylate methyl bromide, 2-dimethylaminoethyl (meth)acrylatemethyl iodide, 2-dimethylaminoethyl (meth)acrylate dimethyl sulphate,3-trimethylammoniumpropyl (meth)acrylamide chloride ((M)APTAC),vinylbenzyl trimethylammonium chloride, diallyldimethylammoniumchloride, 2-dimethylaminoethyl (meth)acrylate (DMAE(M)A), 2-aminoethyl(meth)acrylate, 2-diethylaminoethyl (meth)acrylate,3-dimethylaminopropyl (meth)acrylate,3-dimethylamino-2,2-dimethylprop-1-yl (meth)acrylate,dimethylaminoneopentyl acylate, N-acryloyl sarcosine methyl ester,N-methacryloyl sarcosine methyl ester, 2-N-morpholinoethyl(meth)acrylate, 2-N-piperidinoethyl (meth)acrylate,3-dimethylaminopropyl (meth)acrylamide, 2-dimethylaminoethyl(meth)acrylamide, 2-diethylaminoethyl (meth)acrylamide,N-(4-morpholinoethyl) (meth)acrylamidevinylimidazole, N,N-dimethylvinylbenzylamine, where the amine functional monomers can be quaternised withC₁-C₁₈ alkyl halides such as for example methyl chloride, methylbromide, methyl iodide, dimethyl sulphate, dodecyl bromide, hexadecylbromide. The use of permanently quaternised monomers such as2-trimethylammoniumethyl (meth)acrylate chloride or (M)APTAC is alsopossible.

Preferably block [A] and [B] together comprise 0 to 2 wt % ofmethacrylic acid, more preferably block [A] and [B] together comprise 0to 1 wt % of methacrylic acid and most preferably block [A] and [B]together comprise 0 wt % of methacrylic acid. Preferably the blockcopolymer comprises 0 to 2 wt % of methacrylic acid, more preferably theblock copolymer comprises 0 to 1 wt % of methacrylic acid and mostpreferably the block copolymer comprises 0 wt % of methacrylic acid.

Preferably block [A] comprises 5 to 25 wt % and more preferably 8 to 22wt % of vinyl monomers bearing ionic or potentially ionicwater-dispersing groups not including methacrylic acid.

Preferably block [B] comprises 0 to 15 wt % and more preferably 0 to 10wt % of vinyl monomers bearing ionic or potentially ionicwater-dispersing groups not including methacrylic acid.

Preferably block [A] and block [B] together comprise 3.0 to 18 and morepreferably 3.5 to 15 wt % of vinyl monomers bearing ionic or potentiallyionic water-dispersing groups not including methacrylic acid.

Preferably the vinyl monomers bearing ionic or potentially ionicwater-dispersing groups are selected from the group consisting of 2dimethylaminoethyl(meth)acrylate,3-trimethylammoniumpropyl(meth)acrylamide chloride, acrylic acid,β-carboxyethyl acrylate, itaconic acid and mixtures thereof. Preferablythe vinyl monomers bearing ionic or potentially ionic water-dispersinggroups are anionic or potentially anionic water-dispersion groups.

Preferably the vinyl monomers bearing anionic or potentially anionicwater-dispersing groups are selected from the group consisting ofacrylic acid, β-carboxyethyl acrylate, itaconic acid and mixturesthereof.

Preferred vinyl monomers providing crosslinkable functional groupsinclude hydroxyl functional monomers, epoxide functional monomers, acidfunctional monomers, carbonyl functional monomers or silane functionalmonomers. Examples of vinyl monomers providing carbonyl functionalgroups include acrolein, methacrolein, crotonaldehyde,4-vinylbenzaldehyde, vinyl alkyl ketones of 4 to 7 carbon atoms such asvinyl methyl ketone. Further examples include acrylamidopivalaldehyde,methacrylamidopivalaldehyde, 3-acrylamidomethyl-anisaldehyde, diacetoneacrylate and diacetone methacrylate, and keto-containing amides such asdiacetone acrylamide.

Preferred vinyl monomers providing crystallisable monomers include decyl(meth)acrylate, lauryl (meth)acrylate and stearyl (meth)acrylate.

According to an embodiment of the invention there is also provided anaqueous emulsion comprising a block copolymer obtained by a processaccording to the invention. Preferably the aqueous emulsion has a pH inthe range of from 2 to 11, more preferably 2 to 9, even more preferably2.5 to 8.5 and most preferably 5 to 8.5.

The aqueous emulsions obtained by the process of the present inventionmay be applied to a variety of substrates including wood, board, metals,stone, concrete, glass, cloth, leather, paper, plastics, foam and thelike, by any conventional method including brushing, dipping, flowcoating, spraying, flexo printing, gravure printing, ink-jet printing,any other graphic arts application methods and the like. The aqueouscarrier medium is removed by natural drying or accelerated drying (byapplying heat) to form a coating.

Accordingly, in a further embodiment of the invention there is provideda coating, an adhesive, a polymeric film, a printing ink and/or anoverprint lacquer obtained from the aqueous emulsions obtained by theprocess of the present invention.

The aqueous emulsions obtained by the process of the present inventionmay contain conventional ingredients; examples include pigments, dyes,emulsifiers, surfactants, plasticisers, thickeners, heat stabilisers,levelling agents, anti-cratering agents, fillers, sedimentationinhibitors, UV absorbers, antioxidants, drier salts, organicco-solvents, wetting agents and the like introduced at any stage of theproduction process or subsequently. It is possible to include an amountof antimony oxide in the dispersions to enhance the fire retardantproperties. Optionally, the aqueous emulsions may comprise additionalpolymers not prepared using RITP.

Suitable organic co-solvents which may be added during the process orafter the process during formulation steps are well known in the art andinclude xylene, toluene, methyl ethyl ketone, acetone, diethylene glycoland 1-methyl-2-pyrrolidinone.

Optionally an external crosslinking agent may be added to the aqueousemulsions obtained by the process of the present invention to aidcrosslinking during or after drying.

The solids content of the aqueous emulsions obtained by the process ofthe present invention is preferably within the range of from 20 to 60 wt%, and most preferably within the range of from 30 to 50 wt %.

The present invention is now illustrated by reference to the followingexamples. Unless otherwise specified, all parts, percentages and ratiosare on a weight basis.

In the examples, the following abbreviations and terms are specified:

Solvent=butyl acetateMMA=methyl methacrylate2-HEMA=2-hydroxyethyl methacrylateAMBN=2,2′-azobis-(2-methylbutyronitrile)AA=acrylic acidMAA=methacrylic acidBA=butyl acrylatetBHPO=t-butyl hydroperoxideDMEA=dimethyl ethanolamineIAA=i-ascorbic acid=I₂=iodine

EXAMPLE 1 Block Copolymer Emulsion

Step I

To prepare block [A], a reactor was charged with 395.6 parts of butylacetate, 138.1 parts of methyl methacrylate, 7.2 parts of iodine and16.5 parts of 2,2′-azobis-(2-methylbutyronitrile), and the contents wereheated to 80° C. As soon as the colour of the reaction phase changedfrom brown to yellow, 34.5 parts of acrylic acid were charged to thereactor and the mixture was allowed to polymerise at 80° C. for 6 hours.

To prepare block [B] the reactants comprising 402.7 parts of butylacrylate and 5.4 parts of 2,2′-azobis-(2-methylbutyronitrile) were addedto the solution of block [A]. The mixture was allowed to react for 6hours at 80° C.

Step II

The resultant block copolymer solution was cooled to 60° C. and 34.1parts of dimethyl ethanolamine were added.

Next, the block copolymer was emulsified by adding 440 parts ofdemineralised water.

At this point, the monomer conversion was 97%, corresponding to a freemonomer content of the block copolymer emulsion of 11700 ppm.

Step III

To the block copolymer emulsion obtained after step II) 0.7 parts oft-butyl hydroperoxide and 0.3 parts of water were added. Next a solutionof 1.5 parts of i-ascorbic acid in 29.5 parts of water was added over aperiod of 30 minutes.

15 minutes after the start of the i-ascorbic acid feed, another 0.7parts of t-butyl hydroperoxide and 0.3 parts of water were added. At theend of the i-ascorbic acid feed the emulsion was kept at 60° C. foranother hour after which it was cooled and filtered through a 75 μmfilter cloth.

The final free monomer level was 680 ppm and the solids content was 41%,corresponding to a final monomer conversion of 99.82%.

EXAMPLES 2 TO 6

Block copolymer emulsion were prepared according to the process forexample 1 using components as listed in Table 1 below.

All of the emulsions prepared in Examples 1 to 6 had a particle size inthe range of from 50 to 350 nm.

COMPARATIVE EXAMPLE 1 (CE1)

A block copolymer emulsion was prepared according to the process forExample 1 using components as listed in Table 1 below, where methacrylicacid was used instead of acrylic acid. However the after step II wascompleted the emulsion was extremely unstable and step III could not becarried out.

Results:

The amount of final free monomer and the total monomer conversion isgiven in Table 1 below.

TABLE 1 Example 1 2 3 4 5 6 CE1 Step I Block A Solvent 395.6 395.6 395.6395.6 401.5 384.5 400 AA 34.5 34.5 — 80.5 29.2 28.0 — MAA — — — — — —29.1 MMA 138.1 138.1 — 322.2 — — — 2-HEMA — — 115.1 — — — — AMBN 16.516.5 16.5 16.5 8.4 32.1 16.5 BA — — 172.6 — 262.7 251.6 261.7 I₂ 7.2 7.27.2 7.2 3.6 14 7.3 Block B AA — — 28.8 — — — — BA 402.7 402.7 — 172.6 —— — AMBN 5.4 5.4 5.4 5.4 2.7 10.5 5.4 MMA — — 402.7 — 291.9 279.5 290.8Step II DMEA 34.1 34.1 28.5 79.6 28.9 27.6 24.1 Water 440 440 364 445445 519 519 Conversion % 97 97 96 93 97 97 36 Free monomer ppm 1170011700 13100 26400 11800 10800 241300 Step III tBHP0 0.7 1.5 1.0 1.9 1.11.2 * Water 0.3 0.6 0.4 0.8 0.5 0.5 * IAA 1.5 2.9 2.1 3.8 2.2 2.3 *Water 29.5 59.0 41.9 76.3 44.2 46.4 * tBHPO 0.7 1.5 1.0 1.9 1.1 1.2 *Water 0.3 0.6 0.4 0.8 0.5 0.5 * Final Conversion % 99.82 99.92 99.9299.92 99.92 99.88 * Solids 41 41 35.1 39.6 40.6 39.8 * Final Free 680285 335 290 320 406 * Monomer ppm * = unstable, no further treatmentpossible

1. A process for obtaining an aqueous emulsion comprising a blockcopolymer, which process comprises the following steps: I) solutionpolymerisation of vinyl monomers to obtain block [B] in the presence ofa) a radical precursor; and b) an iodine atom containing block [A]; toobtain a block copolymer comprising at least block [A] and a differentblock [B]; where block [A] and [B] together comprise 0 to 2 wt % ofmethacrylic acid; where block [A] comprises 0 to 25 wt % of vinylmonomers bearing ionic or potentially ionic water-dispersing groups notincluding methacrylic acid; where block [B] comprises 0 to 25 wt % ofvinyl monomers bearing ionic or potentially ionic water-dispersinggroups not including methacrylic acid; where block [A] and block [B]together comprise >2.5 wt % of vinyl monomers bearing ionic orpotentially ionic water-dispersing groups not including methacrylicacid; II) emulsification of the block copolymer obtained in step I);III) performing a post polymerisation reaction on the block copolymeremulsion obtained in step II; and wherein said aqueous emulsion has afree vinyl monomer level <1000 ppm when having a solids content of >20wt %.
 2. A process according to claim 1 where block [A] comprises 5 to25 wt % of vinyl monomers bearing ionic or potentially ionicwater-dispersing groups not including methacrylic acid.
 3. A processaccording to claim 1 where block [B] comprises 0 to 15 wt % of vinylmonomers bearing ionic or potentially ionic water-dispersing groups notincluding methacrylic acid.
 4. A process according to claim 1 whereblock [A] and block [B] together comprise 3.0 to 18 wt % of vinylmonomers bearing ionic or potentially ionic water-dispersing groups notincluding methacrylic acid.
 5. A process according to claim 1 where thevinyl monomers bearing ionic or potentially ionic water-dispersinggroups are selected from the group consisting of2-dimethylaminoethyl(meth)acrylate,3-trimethylammoniumpropyl(meth)acrylamide chloride, acrylic acid,β-carboxyethyl acrylate, itaconic acid and mixtures thereof.
 6. Aprocess according to claim 1 where the vinyl monomers bearing ionic orpotentially ionic water-dispersing groups are anionic or potentiallyanionic water-dispersion groups.
 7. A process according to claim 6 wherethe vinyl monomers bearing anionic or potentially anionicwater-dispersing groups are selected from the group consisting ofacrylic acid, β-carboxyethyl acrylate, itaconic acid and mixturesthereof.
 8. A process according to claim 1 wherein the difference in Tgbetween blocks [A] and [B] is >40° C.
 9. A process according to claim 1wherein said aqueous emulsion has a free vinyl monomer level <800 ppm.10. A process according to claim 1 where the iodine atom containingblock [A] is selected from the group consisting of vinyl polymers,polyurethanes, polyesters, polyethers, alkyds and or mixtures thereof.11. A process according to claim 1 where the iodine atom containingblock [A] is obtained by the polymerisation of vinyl monomers in thepresence of a) a radical precursor and b) iodine or an iodine transferagent.
 12. A process according to claim 1 where the post polymerisationreaction is carried out by the reaction of a redox couple comprising anorganic or inorganic peroxide or hydroperoxide and a reducing agent. 13.A process according to claim 1 where the post polymerisation reaction iscarried out by the reaction of an initiator selected from the groupconsisting of azo functional initiators, organic peroxides, inorganicperoxides or mixtures thereof.
 14. A process according to claim 1 wherethe block copolymer comprises an additional block [C].
 15. An aqueousemulsion comprising a block copolymer obtained by a process according toclaim 1.